Knockdown of chemokine (CXC motif) ligand 12 (CXCL12) inhibits the spontaneous proliferation of bone marrow stromal cells (BMSCs). BMSCs from 3 normal individuals (A) and 3 multiple myeloma patients (B) were transfected with 25 nM CXCL12 siRNA or control siRNA for 24 hr, incubated for up to 72 hr, and subjected to cell proliferation assays. ^a)P<0.05, compared with the control siRNA.